1. Field of the Invention
The present invention relates generally to a rotation sensor for measuring or detecting rotation or angular orientation between first and second or two or more members. More specifically, the present invention relates to a rotation sensor utilizing light reflection and refraction principles. The present invention also relates to a method for sensing the rotation or angular orientation of a first member relative to a second member.
2. Description of the Prior Art
A variety of rotation sensors are currently available in the art for sensing or measuring relative rotation of a rotatable member. One such rotation sensor is an optical encoder. In such a rotation sensor, a matched light source and a photodetector are provided on the opposite sides of a disk. The disk is attached to a shaft which is in turn mechanically coupled to the device whose rotation is to be measured. The disk is provided with a plurality of apertures which vary in radial position as the disk rotates, enabling light to pass through only at certain radii corresponding to its degree of rotation. Optical encoders are commonly available to provide absolute or incremental angle measurement. Although optical encoder rotation sensors function satisfactorily for certain applications, their use in many applications is limited because of size and weight limitations. They are also sensitive to electromagnetic interference (EMI).
Rotation sensors utilizing electrical resolver technology continue to be used in some aircraft applications. Electrical resolvers rely on mutual induction of electrical coils to convey the rotational position. Rotation sensors using this technology are generally quite massive, are usually less accurate and more expensive than sensors using optical encoders, and are also sensitive to EMI.
Resistive potentiometers are also used in some rotation sensors. The principal limitation of this type of rotation sensor is the limited number of cycles per lifetime, particularly with small sensors. Further, the output of the potentiometer, in most applications, requires shielding. Although normally smaller in size than an optical encoder sensors, they are often less desirable for small volume, critical applications because of unreliability and reduced precision. A further major drawback to potentiometer based sensors, like the others described above, is that the signal is conveyed via a wire; therefore, they are not immune to electromagnetic interference (EMI).
Hall effect rotation sensors involving the rotation or movement of a magnet past a detector are also available. However, they likewise suffer from the limitation of not being immune to EMI.
Accordingly, there is a need in the art for a rotation sensor which is small, lightweight, immune to EMI and is accurate and reliable.